Daikin Super Multi NX split system airconditioners and building in hot humid climate

We are moving from a hot dry western climate to warm humid Mackay Qld with high exposure to salt and are building new home conventional brick veneer with rendered concrete brick, vapour barrier exterior wall wrap, non ventilated ceiling with under iron sarking, and insulated external & internal walls and ceiling with insulation batts, I think. Will have six rooms (one larger living area and the rest moderately sized bedrooms and media room) which we would like to air condition separately for efficiency & only the living area, media and main bedroom would be used every day and naturally AC at different times. My main concern and biggest fear is the risk of condensation and mould especially in wall and ceiling cavities where it can’t be controlled later on if the planning is poor. On line research seems to recommend not overpowering AC to make the system work a bit harder and give more run time to remove humidity. To cut down on the number of outdoor units I am looking at the Daikin Super Multi NX multi split systems with Compact Casette in the living area and wall mounted heads in the other rooms and these units also have cooling only versions. I find out that the Daikin AC when operating on the the DRY mode is factory preset at 24 degree C and it concentrates its resources to removing air from the room as well as cooling. We are moderate users of AC and I would like to run the unit at a higher temp combined with ceiling fans to lower the vapour pressure differential to the outside and limit the amount of moisture being pulled into the walls and ceiling from outside the room. Does anyone have any comments or experience and recommendations on these units and of comparable makes and advice as to whether there would there be any problems running only one smaller bedroom AC at night from the large external multi split unit. Also does anyone have experience or comments on fixed dehumidifiers for this situation?


Welcome to the community @Colin5,

I cannot comment on the vast majority of your points, but I have a Daikin split 9.4 Cora and a year later added a 3.5 Altira, in Melbourne.

When we bought the Cora I asked about the multihead units and was informed that they are not fully independent as one might expect. eg an external unit capable of supporting 6 indoor units does not have ‘6 speeds’ although the 6 indoor units can be individually programmed; when one goes on the external unit essentially goes on even if at a fractional capacity. In some products the indoor units seem to be paired for on/off although not for temperature.

That is just a question to ask. Dependant on the answers you might be better off with a different configuration if power consumption is a primary issue. Only running a small indoor head, part of a larger system configuration, in the bedroom could use ‘more of the system’ than you expect.

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Hi @Colin5. Welcome to the community and the tropical north.

Until a few years back we had lived in NQ, including 20 years between Mackay and Townsville as home owners,

@PhilT makes a good observation. Unless you are desperately short of outdoor space, the multi head splits may not be the best solution for your needs. They are typically less efficient overall according to a neighbour who managed the local branch of a national installer and brand distributor. He installed individual inverter units plus solar PV. If like most modern houses yours is more open plan you may also find it more comfortable having all areas of the home at a similar level of coolness (dry more important than temperature).

Our issues with mould were minimal. One house was brick veneer, (IE timber framed with a clay brick non supporting exterior wall). Another was concrete filled masonry cement block, which is structural and supported the roof. Both with batts and tin roof. What we found is it is the locations internally where there is minimal air movement that were more prone to mould.

It’s difficult to comment on your insulation choices as every house is different. With very few exceptions salt spray and sea air would be an odd concern for Mackay, beach front excepted. It’s just very wet and humid for two thirds of the year where ever you live.

If your house has been well designed and constructed there should be no accumulations of condensation internally. Good ventilation and plenty of natural light are your friends. We’d also not put in air conditioning in Mackay without installing a cyclone rated solar PV to power it. If you have a house on slab design with concrete or tiled floors we found the thermal mass helped in the evening, if we cooled the house a little more than we liked in the afternoons. We found 26C comfortable, although some new comers preferred 18-22C until the first power bill arrived.

Externally, it’s the tropics and everything goes mouldy, or more likely grows algae or moss. Simple pool chlorine or bleach can be cheap and effective. Stay too long and some suspect it affects how the locals think and talk (more slowly with an odd turn of phrase often ending in ‘eh’). I’ll be polite there as you can never be sure which of the family are reading this.


Also venting the roof cavity can address much of the moisture build up, eg a whirlybird. Some of the vents come with closure systems so that cyclones or a need to retain heat such as in winter can be easily accommodated.


I am no expert, but I am wondering why you aren’t insulating under the roof. In my opinion, sarking is an adjunct to high R insulation, not a replacement.

The other recommendation is to not put all your eggs in one basked with too many head units off one system. We are in SEQ in a highly corrosive salt/wind environment and were told not to by air conditioning design person, and also the aircon people who came to quote to go for seperate units.

We got the message and ended up putting in multiple outdoor units with only one motor splitting between two rooms because the head units were almost back to back. This way the units were selected based on the size of the rooms they serviced.


Thankyou will go individual splits


Thanks for that will go individual splits. With your brick veneer house what insulation and sarking did you have in the roof space and was the wall cavity or the ceiling space ventilated. From what you say you didn’t have any problems up there. Thanks


thanks I think that would be the trick close them off in winter


Not really sure but will ask about it. Some under iron sarking permits the flow of water vapour from the bottom upwards to allow water vapour to escape the space. But good point thanks.


Our last house in Mackay was a 1990’s design, with open living designed for letting the outside air in or inside air out with good cross ventilation. It was fully screened and was never intended to be an insulated refrigerated box. We only installed air cons in the downstairs office and rumpus room.

With the brick veneer there were ventilation bricks in the walls of the raised portion and drainage slots in the on slab section. My understanding is the cavity needs to have some ventilation to avoid serious issues from damp, hence the drainage slots etc in the brick work.

There was no sarking with the corrugated colour bond roof, 22deg pitch. Ceilings, Earthwool bats R2.5. We had an elevated position facing east with a low westerly aspect. The west facing walls were also insulated with Bradford bats.

Mackay does not get super hot. Summer daytime average 30C and nights 23-24C. It just gets humid. Apologies, to those from cooler places. I go looking for an extra layer if the temps fall below the low 20’s.

We had two other houses in Mackay. Both lowset poorly positioned brick veneer rented houses, prior to building. They had poor natural airflow. The aircons had to work flat out in summer to make life bearable.

P.S. (edit)
Personal preference I’d not build a brick veneer house in the wet tropics again. There are other lower energy options.

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Your comments re cavity drained to bottom & with ventilation tie in with online info CSR Know your cavity part 2.
I’ve tried to block out the west & maximise ventilation with our plan but its not perfect, was going for good insulation and fans and use AC in individual rooms for the extreme. We will be at Sladie with full exposure to the prevailing wind.
What is your preferred construction there if you’re not sick of this? thanks

I’ll assume you are not in the flood zone at the back of ‘Sladie’. If you have experienced a Cat 3 or 4 cyclone or seen what damage even a cat 1 or 2 can do, the answer is to put that as your first and second priorities. The third priority is to not forget the first two. Mackay has not had a direct hit since 1918 (cat 4) if my memory is half reliable. It’s over due for another big one. Apologies, if you already appreciate that observation.

Slab on ground with core filled masonry block would be my basic choice. There are other engineered options that are just as solid, but building different usually costs. Eg precast panels and steel frames corrosion proofed for your prominent location. The biggest concerns are usually the roof staying on, the windows and doors not leaking water, or either failing when they are smashed by flying debris. We witnessed the aftermath of Yasi which was a Cat 5. Nothing more to say.

Hopefully you have a reliable designer/architect. Our experience on that count is the designer will give you a conservative substantial design if you are clear in your needs.

Brick veneer can also be very strong, depending on the frame construction. There are just more points around doors and windows and infills in cheap two story construction that may leak or fail.

IF and it’s a big if, money was not a concern, I’d look for a specialist eco house designer, build in lots of thermal mass with the insulation and cladding on the outside of the main walls. But then you need to consider whether your site is worth the investment.

We are at about 8 meters AHD where a lot of Sladie is 5 M.
I was told that they can make b/veneer as strong as the c block construction but at a bit bigger cost, I’ll re visit that.
We have a fair site but if eco construction or eco builder isn’t already up there it would be beyond me to organise it. Anyway Mark thanks for your help

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If you are going to have plate glass sliding doors and larger windows, try to see if you can get fittings to put up covers in case of cyclones. After being through some cyclones including Althea, I can from experience say plate glass is an invitation to disaster without having some shuttering system. Large panels of glass while allowing more light, once broken allow the roof to leave the house.

You’re welcome. Hope it works out for you.

You might look at the Mackay flood and evacuation zones and check your lot here, if you have not done previously.

Airconditioning a room in a humid environment could cause condensation in the wall cavity if external air an flow into the cavity (think of a fridge cold glass of water and condensation forming on the outside of the glass…the same could happen on the outside of the room’s wall sheeting). I understand that insulation can reduce potential for condensation within wall cavities…

There are established standards for cavity brick construction. The inner structural frame is wrapped in a waterproof building cloth - sarking.

CSR does a better job of explaining what else is important.

It works, providing the design standards are followed by the builder.

Optionally builders can also add insulation in the frames between the studs, the sarking wrapper and typically plasterboard room lining. The greater the temperature differential between inside and outside the greater the benefit.

Unfortunately most of the TV paradigms for a well designed and built house feature cool temperate to cold climate environments. We all have our own ideas of what makes a great home.

Edit added, as Colin5 also noted previously.

Refer https://www.csr.com.au/building-knowledge/building-science/know-your-cavity-part-2

I’ve no financial interest in CSR as an investor or ex employee, although I did once work for one of their competitors, long time ago. A number of well known building materials suppliers provide readily accessible general information and guides to the proper use of their products and more general advice to assist with making product purchase decisions.

Good point, but I’ve been told that garage doors gutters etc have a limited life from rust so I was going laminated glass with moderate sized windows instead of the shutters thanks

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Aluminium gutters as long as they are not matched with iron/steel roofing materials last a long time. Steel/iron causes the aluminium to corrode quickly.

Garage doors with heavy galvanising on unpainted surfaces last well, just maintenance to ensure damage is repaired soonish is important.

I remember quite well the lady on Pallarenda during Althea who had laminated doors and when they went she was lacerated by the glass, luckily there was a Dr next door who was able to save her. I have lived in Townsville, Mackay, worked in Bowen, have rellies in Cardwell and been through a few, I always followed my G’father’s advice to have louvres in preference to windows, if windows try to have smaller panes so if one goes it is only a small hole to fix and if it wasn’t possible then to fit shutters. The lamination may be better these days and so you may have a safe choice there but no harm in looking at having the option to have fittings so that to fit shutters if needed in a storm may not be a large extra cost.

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